1. Field of the Invention
This invention concerns a piezoelectric thin film element, and more particularly concerns the manufacture of ink jet recording heads used in ink jet recording apparatuses.
2. Related Art
In forming piezoelectric thin film typified by plumbum (lead) zirconate titanate (PZT), a piezoelectric thin film is first formed on a substrate by a sputtering method such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or a sol-gel method such as spin coating, and this is subjected to a heat treatment at a high temperature of from 700.degree. to 1000.degree. C.
In seeking to increase the film thickness of piezoelectric thin film, methods attempted have included increasing the accumulation time for film growing and repeating the film growing operation a number of times.
Another method of increasing the film thickness of piezoelectric thin films that is being studied is that of hydrothermal synthesis (known also as "hydrothermal processing"), wherein a reaction for growing the piezoelectric thin film is promoted in a low-temperature environment at 200.degree. C. or lower.
This hydrothermal processing method comprises a seed crystal formation process wherein PZT seed crystals are deposited on the surface of a titanium metal substrate, and a crystal growth process wherein additional PZT crystals are deposited and grown above the PZT seed crystal. This method is set forth, for example, in "Suinetsu goseiho ni yoru PZT kesshomaku no sakusei to sono denki tokusei (Preparation of PZT crystal films by hydrothermal synthesis, and electrical properties thereof)," a research paper recently published in the collected papers presented at the 15th Electronic Materials Research Forum of The Ceramic Society of Japan.
Manufacturing piezoelectric thin films by a sputtering method or sol-gel method requires heat treatment at high temperature, making such methods unsuitable for the fabrication of films of 1.mu. or greater thickness, requiring, as they do, considerably long times for film formation, and, even when thicker films are realized, resulting in problems such as the development of cracks. When a piezoelectric thin film is used as an element employed in an ink jet recording apparatus, film thickness of from 0.5.mu. to 10.mu. or so are preferred. Thus it is needful to prevent the problems noted from occurring. Accordingly, it is possible to employ the hydrothermal processing method wherewith thick films can be made at low temperature, but when this method is used it is very difficult to control the composition of the piezoelectric thin film within an optimal range.
With the hydrothermal method alone, moreover, the crystals in the piezoelectric thin film layer become several .mu. in diameter, whereupon fine, smooth films cannot be obtained, and fine patterning cannot be done, for which reasons deficiencies and other problems arise in the piezoelectric thin films.